JDK-8067661: transferTo proposal for Appendable

[Patrick Reinhart]

Hi Chris & Pavel,

Based on the transferTo Method on the InputStream I would propose to introduce a default method on the Readable interface. In that way the method can be used for all existing implementations of Readable and still be implemented in a special way by a individual implementer.

    /**
     * Reads all characters from this readable and writes the characters to
     * the given appendable in the order that they are read. On return, this
     * readable will be at end its data.
     * <p>
     * This method may block indefinitely reading from the readable, or
     * writing to the appendable. The behavior for the case where the readable
     * and/or appendable is <i>asynchronously closed</i>, or the thread
     * interrupted during the transfer, is highly readable and appendable
     * specific, and therefore not specified.
     * <p>
     * If an I/O error occurs reading from the readable or writing to the
     * appendable, then it may do so after some characters have been read or
     * written. Consequently the readable may not be at end of its data and
     * one, or both participants may be in an inconsistent state. It is strongly
     * recommended that both readable and appendable be promptly closed 
     * if needed and an I/O error occurs.
     *
     * @param  out the appendable, non-null
     * @return the number of characters transferred
     * @throws IOException if an I/O error occurs when reading or writing
     * @throws NullPointerException if {@code out} is {@code null}
     *
     * @since 1.9
     */
    default long transferTo(Appendable out) throws IOException {
    ....
    }


-Patrick